Electric glass furnace



Oct. 29, 1935. J. FERGUSON ELECTRIC GLASS FURNACE Filed Nov. 11, 1933 2Sheets-Sheet l INVENTOR. Ja/r/v fzwe BY KM ATTORNEYs.

1935. J. FERGUSON ELECTRIC GLASS FURNACE Filed Nov. 11, 1953 2Sheets-Sheet 2 ATTORNEYS.

Patented Oct. as, 1935 ELECTRIC GLASS I'UINA John Ind, a corporationFerguson, Indianapolis. edgaerte Fairmount Gla- Worh. lae flnliampelh,

Application November 11, 1983, Serial No. ms

scum.

This invention relates to an electric glass furnace for electricallymelting glass to a molten state as required to manufacture glassware,reference being had to my co-pending application Serial No. 674,303,filed June 5, 1933, entitled Apparatus and process for heating glassfurnace forehearth, which was issued as Patent No. 1,979,- 610 on Nov.6, 1934.

Having in mind the advantages and possibilities inherent in anelectrically heated furnace, as more specifically set forth anddescribed in the above mentioned application, this inventionparticularly pertains to an electric furnace of a circular type whereina plurality of electrodes may be positioned equi-distant about theperiphery of the furnace in contact with the molten glass and connectedwith a multi-phase electric circuit for causing an equal distribution ofcurrent from one electrode to another. Such equal distribution ofcurrent between the several electrodes effects a network of .pathsthrough which the current passes which are well distributed throughoutthe body of the molten glass. Thus, equal heating of the body of moltenglass is obtained and this increases the homogeneity of the product.

In addition to the above, a circular furnace of this type lends itselfto a simple and effective means of feeding the glass therefrom to themolds in the same manner as the well known gob feeder or to a trough forcontinuous feeding. Furthermore, such gob feeding is possible withoutthe use of a forehearth, the usual plunger and such mechanical means asare employed in connection therewith for feeding glass to the molds.This is accomplished in a relatively small furnace of this character byemploying mereLv a discharge orifice in the bottom of the furnace andcontrolling the feed therethrough by variations in pressure applied tothe interior of the furnace which is air sealed. Thus, gobs of glass maybe discharged and controlled in size and shape substantially as in theusual plunger feed or the rate of continuous feed may be similarlycontrolled by maintaining a suitable pressure within the furnace.

In carryins out the invention a relatively small furnace. which ispreferably circular in shape, is provided so that it may be sealed by aclosefitting conical dome. A multi-phase electric circuit is employed toheat the glass contained within the furnace through the medium of aplurality of electrodes spaced around its periphery while the batch maybe fed through a suitable intake opening in the dome. This intake issealed either by the entering batch material or by an air-tight gate andvariations in pressure are effected within the interior of the dome andabove the batch which floats upon the molten glass. Through theopenoriilceinthebottom ofthetankglassmay flow by gravity whenatmospheric pressure or slightly less than atmospheric pressure ismaintained, or may be forced through in gob formation upon alternateincreases and decreases of pressure exerted within the dome. Such flowor g discharge may be retarded in the manner eflected by the plungertype feed by producing a partial vacuum within the tank. For continuousfiow. the interior of the dome is maintained under less than atmosphericpressure, the weight of the molten glass and batch being sufilcient toproduce discharge. Thesurface of the molten glms is thus maintained at asub-atmospheric pressure which permits small gas bubbles or seed to riseto the surface more rapidly and thus facilitates the eliminationthereof.

Another advantage of this character of furnace resides in the ability tocontrol the carbon dioxide gas given off by the batch so that it may besaved and utilized instead of being lost through the stack as in theusual furnace.

The full nature of the invention will be understood from theaccompanying drawings and the following description and claims:

In the drawings. Fig. 1 is a schematic illustration showing a centralvertical section through one form of the furnace and showing thepressure control apparatus applied thereto. Fig. 2 is a section taken onthe line 22 of Fig. 6. Fig. 3 illustrates one form of the electriccircuit employed in said furnace. Fig. 4 is a vector diagram showing therelation'of voltages in the preferred form of multi-phase circuit. Fig.5 is an alternative wiring diagram of electrical connections. Fig. 6 isa central vertical section 85 of an alternative form of the furnace.

In the drawings, there is illustrateda circular glass melting furnacehaving annular side walls Ill within which there is a plurality ofequispaced wells II in each of which there is an elecso trode it. Asshown, herein there are six such electrodes, preferably formed of moltenlead. Surrounding the wells II and extending to a point above theelectrodes I! there are steel Jackets it. Each of the steel Jackets iselectrically connected through a contact I with a lead wire I! to thecircuit, as illustrated in Fig. 3. The wells may have small conduits orfissures formed therein through which the molten lead may pass to makedirect contact with the steel jacket l3.

Centrally of the furnace there is a well l6 for containing the refinedglass above which the molten glass flows over an annular wall or bridgeII into the well and direct contact with the electrodes l2. Thus,through the electric circuit current passes from one electrode toanother above the upper surface of the annular bridge l1 and through thestrata of molten glass contained thereabove for highly heating the sameand so maintaining it in a molten state at the desired temperature.

Supported or floated upon the molten glass there is a batch of materialI! which is to be melted and fed'into the molten glass as the glassisused, so as to automatically maintain a given quantity of molten glassat a predetermined level within the furnace dependent upon the powertransmitted through the circuit. The molten glass and batch are enclosedby a dome I! having its lower peripheral edges supported uponthe uppersurface of the annular wall l0. An air seal is provided between the walland the dome of the furnace which may be accomplished by embodyingwithin the upper surface of the wall an annular metal trough 20 cementedtherein by sodium silicate and containing mercury. The dome is providedwith a downwardly extending peripheral flange 2| which extends into thetrough so as to be surrounded by the mercury to effect the desired seal.

Connected with the' top of the dome there is a batch supply chute 22.The chute is connected with an overhead batch reservoir 23 which is keptfilled .to a suitable depth to maintain the chute 22 completely filledand to maintain the conical pile of batch |8 above the molten glass. Thebatch material within the chute and reservoir effectively preventsingress of air or egress of gases from the furnace. It will be seen fromFig. 1 that the slope of the dome i9 is slightly less than the angle ofrepose of the pile of batch so that a relatively restricted conicalspace 50 is left between the batch and the dome.

Connected with the dome at one side thereof there is a pressurecontrolled conduit 24 communicating with a pressure conduit 25 and avacuum conduit 26 in conjunction with which there is provided a valve21. Conduits 25 and 26 are connected to tanks 5| and 52 respectively,each having a volume preferably somewhat greater than that of the space50. Tank 5| is kept filled with compressed air or carbon dioxide at adesired pressure by a compressor 53 and tank 52 is maintained at asuitable sub-atmospheric pressure by a centrifugal exhaust fan 54. Bymanipulation of the valve 21 to one position, tank 5| is operablyconnected with conduit 24, whereby greater than atmospheric pressure maybe exerted through the conduit 24 to the interior of the dome forforcing refined glass from the bottom of the well is through a dischargeorifice or feeder 28 extending downwardly therefrom. By manipulating thevalve to the opposite position, the tank 52 is connected to the conduit24 for withdrawing air and carbon dioxide from the dome and creating apartial vacuum therein for retarding the flow of refined glass throughthe discharge orifice or withdrawing it upwardly. Thus, by themanipulation of the valve 21 gob feeding of the molds may be efiected inthe same manner as is commonly practiced with the usual plunger type offeed, there being illustrated herein a gob 29 discharged from theorifice and ,severed by the shears 30. An important advantage of thisarrangement is that no forehearth is required for the furnace, the glassbeing fed from the bottom thereof, and no plunger is required whichcauses trouble and breakage when ,used for feeding gobs to produce smallglasstively small capacity of pressure and vacuum tanks.

In the case of a small furnace having a rapid rate of melting and aconsequent rapid rate of evolution of carbon dioxide and other gaseswith- 5 in the furnace it is not necessary to use the pressure tank 5|and compressor 53. Suflicient pressure for extruding a gob of glass maybe generated by the gases evolved from the melting batch by simplyclosing the valve 21. For gob 1 feed in such cases it is only necessaryalternately to close valve 21 to build up a discharge pressure and tomove the same to connect with the tank 52 for exhausting the gas toreduce the pressure. 15

Another advantage of the operation of this type of furnace lies in thefact that the gases given oil in the furnace may be recovered as theyare exhausted from the tank 52 by the fan 54. gases is especiallyvaluable. In order to prevent dilution of the gases to be recovered whenthe pressure tank 5| is in use, the compressor 53 may be arranged tointake from the tank 52 so that no extraneous air is introduced into thesystem. 25

In Fig. 6 there is shown a modified form of furnace which isparticularly equippedforcontinuous feed instead of gob feed and in whichan airtight gate is used to control the batch supply to the furnace. inthe one hundred series refer to parts having a similar construction andfunction to parts indicated by corresponding numbers in the unit seriesin Fig. 1. In this modification, the batch supply through conduit I22 iscontrolled by a 35 suitable gate 55 which may be momentarily opened toadmit the batch and when closed provides an air-tight seal. Whenoperating under certain pressure conditions such a seal is necessaryrather than the material seal illustrated in 4.0 Fig. 1.

v The furnace shown in Fig. 6 is arranged to discharge into a trough 55for continuous feed rather than gob feed and for that reason apparatusfor applying pressure to the interior of the t5 furnace is not needed.The conduit I26 is connected to a vacuum producing device similar tothat illustrated in Fig, l and the rate of discharge is controlled byvarying the operation of the exhaust fan or by throttling the valve I21to produce the proper subatmospheric pressure within the dome M9 for adesired rate of discharge.

A preferred form of circuit connected with the electrodes I2, asillustrated in Fig. 3, may be described as follows: 55

The power mains 30 of a three-phase alternating current supply are deltaconnected to the primary windings 3| of a bank of three similartransformers 32. The secondary windings 33 of said transformers havetheir midpoints con- 60 nected by a common conductor 34 and their outerterminals each connected by one of the conductors i5 to one of theelectrodes i2. Thus, the three-phase primary current is transformed intoa six-phase, star-connected secondary system in 65 which the phaserelation and magnitudes of the voltages at the secondary terminals A, B,C, D,

E, and F are as shown in the vector diagram, Fig. 4, the center 0 ofwhich represents the common conductor 34 considered as at zeropotential. It 70 will be apparent that the voltage between theelectrodes |2 connected to terminals A and C, for example, is the vectordifference of vectors 0A and 0C and is proportional to the distancebetween the. tips of said vectors. Similarly, the 15 The carbon dioxidecontained in the said 20,

In this figure reference numbers 30voltagebetweenanytwooftheelectrodesis proportional to the distancebetween the tips of their corresponding vectors.

The electrodes II are equally spaced about the periphery of the furnaceand, therefore, the distance between any pair of electrodes isproportional to the distance between the corresponding vector tips andis proportional to the voltage between said electrodes. Since theresistance of the charge between two electrodes is proportional to thedistance between them, it follows that a uniform current will pess'fromeach electrode to each of the others. Thus, from each of the sixelectrodes there are five current paths It radiating to the other fiveelectrodes and each path carries a current of the same magnitude as eachof the others.- By this means a symmetrical heating of the mass ofmolten glass is obtained which could not otherwise be obtained in acircular furnace.

Occasionally it is desirable to vary the distribution of the current inthe mass of molten glass as when there is unequal radiation due tovarious causes. For this purpose there are provided switches 30 in thecommon connection 34. When these switches are opened, thestar-connection of the secondary system is broken and only the threediametrical current paths between opposite electrodes are used. Thisresults in a larger concentration of heat at the center of the furnace.Where necessary, the switches 38 may be periodically opened and closed.

In Fig. 5 there is shown an alternative wiring diagram in whichprovision is made for periodically reducing the concentration of heat atthe center. In this diagram, transformers 32 are each provided with apair of independent similar secondary windings it! which arestar-connected in gro p of three by common conductors I34 and i344. Theconnections of terminals A, B, C, D, E, and F of the secondary windingsto electrodes I! are the same as in Fig. 3. A switch lit is arranged toconnect conductors I34 and INA. It is evident that, when switch I isclosed, this winding is the equivalent of that of Fig. 3 with switchesI. closed. and that the same distribution of current will be provided.When switch I is opened. the secondary system is changed to .twoindependent three-phase systems in which only the six current paths itconnecting alternate electrodes are used as shown in Pig. 5. Thus. theconcentration of current at the center of the furnace is reduced.

It-will be evident toone skilled in the arttbatmoreorlessthansixelectrodesmaybe provided, depending upon the sizeof furnace desired and may be connected to suitabletransformersecondarysystemsofagreaterorless number of phases to producecurrent distributions similar to those illustrated herein.

This type of furnace is particularly adaptable for use in themanufacture of small glassware. or for filling small ordersrequiringrapid turnover of the furnace capacity, or different colored'glass.Byvariationofairpressureupontheglassitself within the air-tight dome ofthe furnace. the usual gob feeding may be obtained. However, wheredesired, continuous fiow feeding may be employed and controlled byvariations of tank pressure. Any suitable means may be employed forautomatically controlling the valve II toobtainthedesiredresuitsinfeeding.AsanexampleofvacmnncontroLapartialvacuummay beobtainedinthefurnacewhichmayvaryfrom one-half an inch of mercury in three inches.With a total depth of glass and batch of twelve to fifteen inches in thefurnace, the vacuum res quired to stop the fiow of glass from theorifice will be substantially three inches of mercury. Where it isdesired merely to control the amount of a steady glass stream, a steadyvacuum only will be required, adjusted to the proper value. 10

The partial vacuum may be obtained by the use of an ejector which wouldrender available for conservation and use the carbon dioxide gas givenof! by the batch. which gas would be discharged through the conduits and{6. The is gas may also be recovered by connecting the discharge conduit51 of the blower 54 to any suitable recovery apparatus. Thus, there maybe obtained from the furnace approximately 200 pounds of carbon dioxidegas for every ten of 20 batch melted, which is readily separable fromthe small amount of air entrained with the batch supply, whereupon thegas may be condensed in the usual manner for commercial use.

The invention claimed is: 25

1. An electric furnace for melting glass, including an annularreservoir, a plurality of wells formed about the periphery of thereservoir and spaced from each other, an electrode of molten metal ineach of said wells, a centrally posi- 80 tioned annular well separatedfrom said first mentioned wells by a circular bridge, said wells beingadapted to contain molten glass having its level extending over saidbridge. a discharge orifice communicating with the bottom of the anasnular well through which the molten glass contalned therein may pass, amulti-phase circuit connected with said electrodes, means for generatingcurrent in said circuit, a dome supported over said reservoir to providean air-tight closure 40 therefor, means for feeding batch materialthrough said dome onto the surface of the molten glass, and a conduitconnected with said dome communicating with the interior thereof forvarying the gas pressure therein to control the discharge of moltenglass through said orifice.

2. An electric furnace for melting glass, including an annular reservoirhaving an annular trough formed in the upper surface of its wall,

a plurality of wells formed about the periphery of the reservoir andspaced from each other. an electrode of molten metal in'each of saidwells, a centrally positioned annular well separated from said firstmentioned wells by a circular bridge. said wells being adap ed tocontain molten 66 glass having its level extending over 'said bridge, adischarge orifice communicating with the bottom of the annular wellthrough which the molten glam contained therein may pass, a multi-phasecircuit connected with said elec- 00 trodes, .means for-generatingcurrent in said circuit, a sealed dome moimted over said furnace andhaving its annular lower edges extending in said trough. means forsealing the dome therein soastorendertheinteriorofthefurnaceair-M tight,means for feeding batch material through said dome onto the surface ofthe molten glass.

and a conduit connected with said dome communicating with the interiorthereof for Varying the gas pressure therein to control the discharge of70 molten glass through said orifice.

v JOHN lIB-GUBON.

